Phase Variations and Layer Epitaxy of 2D PdSe₂ Grown on 2D Monolayers by Direct Selenization of Molecular Pd Precursors

Abstract

2D materials and van der Waals heterostructures with atomic-scale thickness provide enormous potential for advanced science and technology. However, insufficient knowledge of compatible synthesis impedes wafer-scale production. PdSe 2 and Pd 2 Se 3 are two of the noble transition-metal chalcogenides with excellent physical properties that have recently emerged as promising materials for electronics, optoelectronics, catalyst, and sensor. This research presents a feasible approach to synthesize PdSe 2 and Pd 2 Se 3 with inherently asymmetric-structure on honeycomb lattice 2D monolayer substrates of graphene and MoS 2 . We directly deposit a molecular transition-metal precursor complex on the surface of the 2D substrates, followed by lowtemperature selenization by chemical vapor flow. Parameter control leads to tuning of the material from monolayer nanocrystals with Pd 2 Se 3 phase, to continuous few-layer PdSe 2 films.Annular dark-field scanning transmission electron microscopy (ADF-STEM) reveals the structure, phase variations and heteroepitaxy at the atomic level. PdSe 2 with unconventional interlayer stacking shifts appeared as the kinetic product, whereas the bilayer PdSe 2 and monolayer Pd 2 Se 3 are the thermodynamic product. The epitaxial alignment of interlayer rotation and translation between the PdSe 2 and underlying 2D substrate were also revealed by ADF-STEM. These results offer both nanoscale and atomic-level insights into direct growth of van der Waals heterostructures, as well as an innovative method for 2D synthesis by predetermined nucleation.

Atomic-Scale Insights into the Lateral and Vertical Epitaxial Growth in Two-Dimensional Pd2Se3–MoS2 Heterostructures

“…The overall synthesis process of the Pd 2 Se 3 –MoS 2 heterostructure is illustrated in Figure a and is based on the methods reported in ref . First, MoS 2 was synthesized on the SiO 2 /Si substrate using chemical vapor deposition (CVD) with a two-zone furnace.…”

“…Monolayer Pd 2 Se 3 shows higher thermoelectric efficiency than other monolayer TMDs . Recently, Tai et al successfully synthesized PdSe 2 and Pd 2 Se 3 on honeycomb lattice 2D monolayer substrates of graphene and MoS 2 , showing epitaxial alignment to the underlying host 2D materials . However, these studies were limited to island domains that were free from lateral in-plane bonding.…”

Applications of 2D-Layered Palladium Diselenide and Its van der Waals Heterostructures in Electronics and Optoelectronics

“…The PdSe 2 has been deposited over the support of graphene or MoS 2 in an epitaxial growth fashion [ 22 ]. The precursor of Pd containing organic molecules has been employed for the formation of PdSe 2 .…”

“…PdSe 2 -based van der Waals heterostructures (vdWHs) have been widely incorporated in current rectifier, polarized light photodetector, and infrared image sensor applications. First, the direct synthesis of PdSe 2 -based vdWHs has been investigated via deposition of PdSe 2 over other 2D materials such as graphene [ 21 ], MoS 2 [ 22 ], MoSe 2 [ 23 ], GeSe [ 24 ], and SnSe 2 . The stacking with arrayed nanomaterials gives rise to heterostructure devices such as ZnO nanorods and Si nanowires [ 25 ].…”

Machine learning in scanning transmission electron microscopy

“…One example is a metal precursor incorporating a bulky organic ligand around a metal to suppress the formation of 3D atom clusters on the 2D support at elevated temperature and yield 2D clusters with flat surfaces and single metal atoms after annealing. 284 Various reports where the epitaxial interactions between the metal nanoclusters and the substrates are analyzed by STEM imaging include the growth of 2D palladium diselenide nanocrystals on monolayer molybdenum disulfide 285 , monolayer lead iodide nanodisks on graphene 286 , a 2D molybdenum diselenide film on hexagonal boron nitride 287 and pyrochlore Nd2Ir2O7 grown on yttria-stabilized zirconia 288 .…”